The present invention relates to a method for treating perfluorocompound (PFC) gas, and an apparatus thereof.
PFC a general term of CF4, C2F6, C3F8, SF6, NF3, and the like. PFC gas is used as an etching gas for semiconductor, a cleaning gas for semiconductor, an insulating gas, and others. The PFC gas is a kind of earth warming-up gas, and its release to atmosphere is an object of regulation. Therefore, various methods for decomposition of PFC have been investigated. One of the methods, wherein PFC gas is decomposed by hydrolysis; subsequently, the decomposed gas is treated with water or an alkaline aqueous solution; and the treated gas is exhausted to atmosphere; has been disclosed in JP-A-11-70322 (1999).
During study of the PFC treating method, wherein the PFC gas is decomposed; the decomposed gas is washed; and the washed gas is exhausted; the inventors of the present invention have found that exhaust blowers and exhaust pipe for exhausting the washed gas are corroded with the washed gas.
The present invention is aimed at suppressing the corrosion of the exhaust blowers and the exhaust pipe with the washed PFC decomposed gas in the method or the apparatus for treating the PFC decomposed gas.
The gist of the present invention is in exhausting the PFC decomposed gas after washing the PFC decomposed gas and separating mist containing PFC decomposition products contained in the decomposed gas.
The inventors of the present invention have found that the corrosion of exhaust pipe and exhaust blowers is caused by the PFC decomposed gas; which has not removed by washing in the washing step, releasing to outside of the washing tower accompanied with mist, and adhering to the to the exhaust blower or the exhaust pipe. Therefore, the inventors have succeeded in suppressing the corrosion of the exhaust pipe and the exhaust blowers by separating the mist from the washed PFC decomposed gas.
A large proportion of the mist contained in the gas after the washing step have mainly a particle size larger than 10 μm, and the mist having a particle size smaller than 1 μm are utmost a several tens percent. In order to remove the mist having such a particle size distribution, cyclone separators, filter separators, electric dust collectors, active carbon adsorption apparatus, and the like are suitable. In particular, the cyclone separators and the filter separators are desirable, because their apparatus can be made small size. When the filter separator is used, it is desirable that plural filters having different pore sizes each other are overlapped, and large size mist is separated by the filter having larger pore size and small size mist is separated by the filter having smaller pore size. If only the filter having smaller size is used, passing the gas through the filter is disturbed. Then, it is not desirable, because the pressure loss at the filter is increased, and use of large size blowers is required. The pressure loss can be restricted to small by combining plural filters having different pore sizes each other.
The present invention can be applied to a method, wherein the PFC gas is decomposed by hydrolysis, oxidation decomposition, combustion, or thermal decomposition, and the like to a gas containing hydrogen fluoride, and washed and exhausted. In addition to the above method, the present invention can be applied to any methods, if the method decomposes PFC gas to the gas containing hydrogen fluoride. In accordance with converting PFC to hydrogen fluoride, the hydrogen fluoride can be removed from the gas by absorbing into a solution by washing with water or an alkaline aqueous solution, and the gas released from the washing tower can be made a gas which substantially does not contain fluoride compounds.
Prior art, wherein the mist is separated from the exhaust gas after washing the exhaust gas, is disclosed in JP-A-11-216455 (1999), but the prior art is not aimed at treating the PFC decomposed gas. JP-A-8-318122 (1996) and JP-A-57-197023 have disclosed methods, wherein an absorption tower is installed after water washing apparatus in the process, but the prior art are not aimed at treating the corrosive mist of PFC decomposed gas, neither.